Variable frequency electric fence charging circuit

ABSTRACT

A variable frequency electric fence charging circuit for supplying charge pulses to a conductive fence wire at selected frequencies adapted to the particular livestock to be restrained comprises a firing circuit utilizing a silicon controlled rectifier connected to the primary winding of a step-up transformer and connectable to an alternating current source to deliver a charging pulse through the transformer to a fence wire when the silicon controlled rectifier is made conducting by a triggering circuit. The triggering circuit includes an oscillator with its output connected to the gate of the silicon controlled rectifier to selectively, periodically open the gate to permit current flow from the alternating current source to the primary winding of the transformer, inducing a high voltage in the secondary winding which is applied to the fence wire. The time constant of the oscillator may be varied by the operator to produce two distinct oscillator frequencies, permitting use of the frequency best adapted to the livestock to be restrained. The triggering circuit energizes the oscillator in synchronization with the alternating current source to assure that the oscillator opens the gate only when the alternating current source nears a peak voltage magnitude to assure high voltage being applied to the transformer primary. The charging circuit is protected from lightning or other high voltage transients reaching it from either the fence wire or the alternating current source.

United States Patent I 1 Caron [451 Feb. 25, 1975 VARIABLE FREQUENCY ELECTRIC FENCE CHARGING CIRCUIT [75] Inventor: Thomas E. Caron, Crystal, Minn.

[73] Assignee: Sta-Tite Corporation, Plymouth,

Minn.

[22] Filed: Sept. 10, 1973 [21] Appl. N0.: 396,076

[51] Int. Cl.. 1105b 37/02, 1-105b 39/04, H05b 41/36 [58] Field of Search 315/200, 206, 209, 219, 315/276, 287; 256/10; 174/137 [56] References Cited UNITED STATES PATENTS 2,567,667 9/1951 Hanghett, Jr. 256/10 X 3,201,597 8/1965 Balan 315/200 R 3,377,125 4/1968 Zielinski 315/209 R 3,581,299 5/1971 Schmit 256/10 3,600,996 8/1971 Switsen 315/200 R 3,655,994 4/1972 Malme 256/10 3,655,995 4/1972 Malme 256/10 3,772,529 11/1973 Boeing 256/10 [5 7] ABSTRACT A variable frequency electric fence charging circuit for "supplying charge pulses to a conductive fence wire at selected frequencies adapted to the particular livestock to be restrained comprises a firing circuit utilizing a silicon controlled rectifier connected to the primary winding of a step-up transformer and connectable to an alternating current source to deliver a charging pulse through the transformer to a fence wire when the silicon controlled rectifier is made conducting by a triggering circuit. The triggering circuit includes an oscillator with its output connected to the gate of the silicon controlled rectifier to selectively, periodically open the gate to permit current flow from the alternating current source to the primary winding of the transformer, inducing a high voltage in the secondary winding which is applied to the fence wire. The time constant of the oscillator may be varied by the operator to produce two distinct oscillator frequencies, permitting use of the frequency best adapted to the livestock to be restrained. The triggering circuit energizes the oscillator in synchronization with the alternating current source to assure that the oscillator opens the gate only when the alternating current source nears a peak voltage magnitude to assure high voltage being applied to the transformer primary. The charging circuit is protected from lightning or other high voltage transients reaching it from either the fence wire or the alternating current source.

6 Claims, 1 Drawing Figure s/ ,ta 32 VARIABLE FREQUENCY ELECTRIC FENCE CHARGING CIRCUIT BACKGROUND OF THE INVENTION Prior to the invention, electrical fence chargers utilized a single frequency at which high voltage pulses were applied to the conductive fence wire. While the use of a single charging frequency on the order of 30 to 40 shocks per minute has been found acceptable for certain livestock such as cattle, it has often been ineffective for control of less responsive livestock such as hogs. Hogs encountering the fence and receiving a sin gle shock often accelerate toward the fence, tearing it loose or damaging it before the next charging pulse is applied. Accordingly, it is desirable that a fence charging circuit be able to deliver charging pulses to the fence at a plurality of frequencies so as to permit an operator to select a higher or lower frequency best adapted to particular livestock to be restrained.

Another shortcoming of the known fence chargers is that many fail to deliver a consistently high voltage charge to the fence, and with lowering voltage levels the charge on the fence wire may become ineffective, particularly where long fence lines are utilized. A principal reason for the decreasing magnitude of voltage applied to the fence wire is that the commonly utilized sinusoidal alternating current is applied to the primary winding of the transformer at a time when the alternating current voltage is near zero. Most chargers operate by applying the A.C. line voltage to the transformer primary at regular intervals defined by a vibrator or oscillator, but do not consistently apply the A.C. voltage when the voltage is at its peak value; often the line voltage is applied to the fence when it is of low or zero magnitude, producing an inadequately charged fence.

It has been found highly desirable to use solid state circuitry in a charger due to its long life, high resistance to shock and rough handling, and minimum energy consumption. While offering these advantages, the components used in such circuits can be extremely sensitive to large voltage transients delivered to the circuit from either the fence wire or the power source. Such transients are not uncommon and are most frequently generated by lightening striking power lines, fence wire or adjacent the wire to induce high voltage which eventually reach the fence charger circuit. For solid state circuitry to be effective in an electric fence charger, the circuitry must survive such high voltage transients.

BRIEF SUMMARY OF THE INVENTION The invention relates to the field of electric fence charging circuits and comprises a variable frequency charging circuit which is fully protected from high voltage transients striking the circuit from either the fence wire or the alternating current power source. In addition the charging circuit utilizes a triggering circuit which assures that a firing circuit is actuated to energize the fence from an alternating current source only when the alternating current source nears a peak voltage magnitude, thereby delivering consistently high voltage to the transformer for charging the fence.

The fence charging circuit utilizes a firing circuit which includes a silicon controlled rectifier connected in series with the primary winding of a step-up transformer, a voltage pulse from an alternating current source passing through the silicon controlled rectifier to the. primary winding when the gate of the rectifier is opened by a pulse from the triggering circuit. As voltage is applied to the primary winding, it induces a substantially higher voltage in the secondary winding which is then applied to the conductive wire of the fence.

The triggering circuit includes an oscillator with its output electrically connected to the gate of the silicon controlled rectifier to selectively open the gate each time the oscillator produces an output pulse. Means are provided on the oscillator for selectively establishing a plurality of oscillator output frequencies, permitting the operator to select a frequency better adapted for controlling the particular livestock to be contained within the fence. The preferred frequency may be set and the oscillator then delivers pulses at the selected frequency rate to the gate of the silicon controlled rectifier, causing the firing circuit to energize the transformer primary at the frequency of the oscillator.

To assure the triggering circuit opens the gate only when substantially peak voltage of the alternating current source is applied to the firing circuit, the oscillator is energized in synchronization with the alternating current source by means of a diode and capacitor connected in parallel with one another and in series to the input of the oscillator, the diode being energized by the alternating current source.

To assure the charging circuit is not damaged by high voltage line transients from the alternating current source, a varistor is connected across the input terminals of the firing circuit to provide a shunt across which high voltage transients may be shunted, thereby protecting the firing circuit from lightning and various other power irregularities. Because lightning may also strike the electrical fence wire and reach the charging circuit through the transformer, special precautions have been taken to prevent such occurrences. The secondary winding of the transformer is connected to earth ground and a capacitor is connected between its output terminals to shunt most high voltage transients directly to ground. In addition the laminated core of the transformer is grounded in the event that exceptionally high energy transmitted to it should cause melting and breakdown of the insulation between the laminated plates.

To aid an operator in determining whether the triggering circuit is functioning properly a combined triggering and monitoring device is used in the triggering circuit, permitting an operator to visually determine that the triggering circuit is delivering a pulse to the gate of the silicon controlled rectifier.

The charging circuit is extremely reliable, long lasting, easy and inexpensive to manufacture and effective with all livestock. It delivers a regularly spaced, unusually high voltage charge to the fence without any notable decrease in voltage since the triggering circuit is continually synchronized with the alternating current source. It is protected from the high voltage transients reaching the semiconductor components from the power source or the fence line.

These and other objects of the present invention will become apparent from the following detailed description of the invention and from the appended drawing and claims.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a schematic electrical circuit diagram of the electric fence charging circuit shown connected between a fence and a standard AC. power source.

MAIN DESCRIPTION Referring now to the drawing, the variable frequency electric fence charging circuit which may utilize a printed circuit board has input terminals 12 and 14 connected across a sinusoidal voltage source 16 such as commercially available 110 volt, 60 cycle alternating current. The terminal 17 is a standard third wire ground to reduce the danger of dangerous electrical shock to an operator.

For purposes of description in this disclosure, it shall be presumed that terminal 12 is the so-called hot wire of the voltage source 16 and that terminal 14 is neutral, being at substantially ground potential. Input terminal 12 is connected through conductor 18 to a ballast resistor R5 which is connected in series by conductor 19 to diode D1, which in turn is connected in series by conductor 20 to the primary winding 22 of the step-up transformer 24. Conductor 26 interconnects the primary winding 24 to the anode of a silicon controlled rectifier SCR, whose cathode is connected in series with conductor 28 which leads to input terminal 14.

Conductor 29 extends from conductor 20 to capacitor C3 which is connected in parallel with the diode D1. Conductor 30 extends from capacitor C3 to conductor 31 which terminates at capacitor C2. Conductor 32 extends from capacitor C2 to the terminal 34 of the secondary winding 36 of transformer 24. Terminals 34 and 38 constitute the output terminals of the charging circuit 10, and terminal 34 is connected to an earth ground 39 while the remaining output terminal 38 is connected directly to a conductive fence wire 40 which is to be charged.

Conductor 18, resistor R5, conductor 19, diode D1, conductor 20, transformer 24, conductor 26, silicon controlled rectifier SCR, conductors 28, 29 and 30 and capacitor C3 collectively comprise a firing circuit through which current from the AC source 16 is conducted to charge the fence when the SCR is conducting. The diode D1 serves as a half-wave rectifier to provide positive voltage pulses for charging the capacitor C3, which discharges across the primary winding 22 of the transformer 24 when the SCR becomes conducting. A triggering circuit which includes an oscillator is used to open and close the silicon controlled rectifier SCR by means of periodic output pulses delivered to the gate 43 of the rectifier as will now be described.

An oscillator circuit 42 has at its output terminal connected to the gate 43 of the SCR. The circuit 42 includes resistors R7 and R6 connected in parallel with one another and to alternate terminals 46 and 48, respectively, of the single pole double throw switch 44. A conductor 50 extends from the parallel resistors R6 and R7 to resistor R1 which is series connected with neon bulb N through conductor 52. A conductor 53 extends to the positive side of a capacitor C1 whose negative terminal is connected by conductor 54 to the conductors 30 and 31, which are connected through conductor 28 to ground. A biasing resistor R3 is connected between conductors 54 and 56 to provide biasing for the SCR thereby keeping the gate 43 in a closed condition at all times other than when the oscillator 42 pulses it to an on condition. Resistor R2 is connected between conductor 54 and conductor 50 and along with resistor R1 forms a voltage divider. The resistors R1 and R2 are interconnected by conductor 58. Accordingly, the selectively variable frequency oscillator circuit 42 includes switch 42, resistors R7, R6, R1, R2, capacitor C1 and neon tube N connected to the gate 43 of the SCR by conductor 56, the recited components being electrically connected as shown in the drawing.

The output frequency of the oscillator '42 is determined by the value of the resistor placed in series between switch 44 and conductor 50. By varying the value of the resistors R7 and R6 which constitutes first and second impedance elements, the time constant of the oscillator may be controlled to provide output frequencies well adapted to various livestock. The preferred output frequencies of the oscillator 42 are approximately 1.3 cycles per second and 0.6 cycle per second. These frequencies result in the delivery of a charge to the fence wire at approximate intervals of /1 and 1% seconds, respectively. The delivery of a charge to the fence at second intervals has been particularly effective for the control of hogs, while the delivery of charges at intervals of 1% seconds has been effective for most other livestock. Accordingly the switch 42 is set for the charging frequency best suited to control the type of livestock present.

The triggering circuit includes the already described oscillator 42 as well as diode D3 connected to conductor 19 by conductor 60 and to switch 44 by conductor 62. The capacitor C5 is connected in parallel with diode D3 by conductor 64 extending from conductor 62 and by conductor 66 extending from conductor 30 to the capacitor.

The diode D3 and capacitor C5 are part of the triggering circuit and provide a means for delivering halfwave rectified current from the conductor 19 to the oscillator 42 in synchronization with the alternating current source 16 thereby assuring that the oscillator 42 opens the SCR only when the voltage of the alternating current source 16 is near its peak value. This assures that the voltage applied to the primary winding 22 of the transformer 24 is consistently high.

The triggering circuit also includes resistor R3 connected between conductors 54 and 56, the resistor R3 biasing the gate 43 of the SCR to keep the SCR in an off condition unless the oscillator 42 is pulsing it to an on condition.

Because lightning flashes may occasionally strike the power line along which the alternating current is delivered to the input terminal 12 and thereby introduce high voltage transients on the line or because such transients may be occasionally introduced by power generation irregularities, it is desirable to provide protection for the SCR in the firing circuit in the event such pulses reach the circuit 10. To prevent these high voltage spikes from damaging the SCR a varistor 70 is connected in shunt across the input terminals 12 and 14 of the firing circuit. The varistor 70 is a semi-conductor device with a voltage dependent nonlinear resistance that drops off markedly as the voltage across the varistor is increased. At ordinary voltage levels at or below volts the varistor is substantially non-conducting. However. when the voltage exceeds a pre-determined value which may be approximately volts, current flows readily through the varistor 70 and during brief intervals the varistor is capable of absorbing considerable power and dissipating it in the form of heat. Accordingly, sharp voltage spikes lasting a'few microseconds in duration are not damaging to the firing circuit since these high voltage spikes are absorbed in the varistor 70 and dissipated, accordingly protecting the firing circuit from lightning and high voltage transient phenomena at the input terminals.

The charging circuit may also be protected from high voltage transients caused by lightning striking the conductive wire 40 or adjacent thereto and inducing brief but substantial voltages. While the transformer 24 provides some isolation to' the remainder of the firing circuit, it has been found desirable to provide additional protection by connecting capacitor C4 across output terminals 34 and 38 of the secondary winding 36 to provide a path for fast transients to ground 38, thereby diverting a substantial portion of the energy of the transient voltage to ground and preventing its entry into the secondary 36. In addition, a conductor 32 extends from the secondary winding 36 and is connected through capacitor C2 to conductor 31 which is connected to ground 14through conductors 30 and 28. Accordingly a component of a high voltage transient from the fence wire 40 may be conducted along the line 32 and blocked by the capacitor C2.

A further safeguard for the semiconductor devices in circuit is provided by grounding the laminated core 72 of the transformer 24 through conductor 74 to the third wire ground. Accordingly, high energy pulses from the fence which may enter the secondary winding 36 of the transformer and generate such intense heat as to cause breakdown of the insulation separating the laminated core elements will be transmitted to ground along the conductor 74, thus providing further protection and isolation to the remainder of the firing circuit 10. I

Because electric fence charging circuits often generate radio and television noise interference, it is desirable to include a noise filter in the charging circuit 10. Diode D2 and resistor R4 are connected in series with one another and in parallel with the silicon controlled rectifier SCR across conductors 26 and 30. The noise filter defined by the diode D2 and resistor R4 effectively protect adjacent television and radio reception from unwanted interference.

While a range of values may be applied to the shown electrical and electronic components in the circuit 10, the following particular values have been found unusually effective and produce highly desirable results: Capacitor Cl: 1 microfarad, 200 volts Capacitor C2: 0.0033 microfarad, 600 volts Capacitor C3: 30 microfarad, 150 volts DC, electrolytic Capacitor C4: 500 picofarad, KV. DC Capacitor C5: 1 microfarad, 200 volts Diodes D1, D3: silicon diode, 1 amp, 400 volts Diode D2: silicon diode, glass passivated, 1 amp 300 volts Varistor, 130 volts, 20 joules at 1250 amps Resistor R]: 1.5 megohms, 1% watt Resistor R2: 100 K ohms, k watt Resistor R3: 1000 ohms, 1% watt Resistor R4: 10 ohms, 9% watt Resistor R5: 500 ohms, 5 watt Resistor R6: 100 K ohms, /2 watt Resistor R7: 82 K ohms, V; watt In operation, the output terminal 34 of the secondary winding 36 is carefully grounded to earth at ground 39 and the conventional three-prong electrical plug is in serted into a receptacle wired to a standard 60 cycle 1 10 volt alternating current source 16.

Alternating current from source 16 flows along conductor 18 passing through resistor R5 and splitting at junction to flow along conductors l9 and 60. Alternating current flowing along conductor 19 passes through diode D1 and is half-wave rectified, only the positive half-wave of the current passing through the diode. The half-wave rectified current flows along con ductor 20 and then along conductor 29 charging capacitor C3 and then returning along conductors 30 and 28 to input terminal 14 which is grounded. No current flow occurs along conductor 20 to the primary winding 22 of the transformer 24 until the silicon controlled rectifier SCR becomes conducting, as will be described hereafter. The capacitor C3 charges rapidly, and its stored energy is discharged across the primary winding 22 of the transformer when the silicon controlled rectifier becomes conducting.

Current flow from junction 75 along conductor 60 passes through the diode D3 and is rectified, eliminating the negative half cycle of the alternating current. The remaining positive half cycle flows along conductor 62, splitting at junction 77, a component flowing to conductor 64 to charge capacitor C5, then flowing through conductors 66 and 30 to conductor 28 and ground. Current leaving the diode D3 along with a discharge current from the capacitor C5 provides energy to the oscillator along conductor 62. The current to the oscillator from the diode D3 and capacitor C5 synchronizes the oscillator 42 to produce an output frequency in synchronization with the alternating current source 16, thereby assuring that the output frequency pulses of the oscillator are applied to the gate 43 of the SCR at times when substantially peak magnitude of the alternating current voltage is reached.

The operator positions the switch 44 in the position best adapted to the control of the particular livestock to be encountered at the fence. For example, if cattle are to be contained within the fence enclosure, the switch 44 may be placed in the slow" position where current from conductor 62 passes from switch 44 through resistor R7 to conductor 50. When this switch arrangement is utilized, the oscillator assumes a time constant producing a frequency of operation of approximately one pulse every 1% seconds. This frequency is excellent for control of cattle.

lf hogs are to be contained in the fence enclosure the switch 44 should be set at the fast position to permit current to flow from the switch through resistor R6 to conductor 50. This setting results in an output pulse being generated by the oscillator 42 at intervals of approximately three-fourths of a second, a frequency well adapted to the containment of hogs and other livestock unresponsive to a slower shock frequency.

As will be appreciated by those skilled in the art, the combination of either resistor R6 or R7 and capacitor C1 determines a particular time constant for the oscillator 42 and defines the output frequency of the oscillator. Current from conductor 50 flows through resistor R1 to charge capacitor C1 with rectified charging pulses delivered to the oscillator. The charged capacitor Cl discharges across neon tube N as the tube N fires in response to its ignition voltage being reached.

When the tube fires, current flows along conductor 52 through the tube and conductor 56 to the gate 43 of the SCR, causing the SCR to become conducting during the interval in which the pulse is applied to the gate. After capacitor C1 discharges, the current flow through the neon tube N stops and the SCR ceases to be conducting. At this point the capacitor C1 recharges, again discharges across the neon tube N as before and continues to repeat this cycle to provide an output oscillator frequency which is periodically applied to the SCR gate 43 to bias the SCR to an open or on condition.

Use of the neon tube N is particularly desirable in the oscillator circuit because each time the neon tube fires, it provides a positive visual indication that the circuit is operating effectively while simultaneously providing the triggering device. Accordingly this combined monitoring and triggering device provides a reliable means for discharging the capacitor C1 and reduces overall cost by eliminating the requirement of a separate indicator device.

As soon as the SCR becomes conducting in response to a pulse from the oscillator 42being applies to gate 43, current flows from the AC. source 16 along conductor 18, through resistor R5, conductor 19, diode D1, and conductor 20 to the primary coil 22 of the transformer 24, passing back to the ground 14 through conductors 26, the now conducting SCR, and conductor 28. Simultaneously, the charged capacitor C3 discharges across the primary winding 22 to further increase the voltage delivered to the primary winding 22. The voltage across the primary winding induces a substantially higher voltage in the secondary winding 36, charging the capacitor C4 which then discharges across the conductive fence wire 40 to provide a high voltage level on the fence. Output voltages in excess of 20,000 volts have been obtained with the disclosed charging circuit to provide a highly effective means for containment of livestock.

During normal operation of the fence, no radio or television noise interference is produced due to the diode D2 and series connected resistor R4 which are connected in parallel with the SCR, thus eliminating ringing phenomena which might otherwise generate television and radio noise interference.

In the event lightning strikes the incomingpower lines and reaches the input terminals 12 or 14 of the charging circuit 10, the high voltage spike associated with such lightning transients actuates the varistor 70, and in response the varistor becomes a substantially short circuit, passing the incoming transient current to ground and preventing its further entry into the circuit 10. Accordingly, the circuit 10 is completely protected against high voltage transients or line irregularities which reach the input terminals 12 or 14 of the circuit.

If lightning should strike the conductive fence wire 40 and generate a high voltage transient at the output terminals 34 and 38 of circuit 10, a major portion of the voltage spike will pass through capacitor C4 to ground fence line is provided by grounding the laminated core 72 of the transformer along conductor 74 to ground. lf the lightning induced voltage transient is so high as to still reach the transformer secondary winding 36 and 38. In the event the voltage transient is of unusual magprovides sufficient heat to break down the insulation between the laminations of the core 72, the charge is passed from core to ground along the conductor 74, thereby providing still further protection to the remainder of the firing circuit 10 and the semiconductor components therein.

Accordingly the variable frequency fence charging circuit 10 provides a highly reliable and safe circuit for energizing an electric fence at frequency levels adapted to the particular livestock to be restrained. The use of diode D3 and parallel capacitor C5 assures that alternating current is applied to the primary coil of the transformer only when the alternating current voltage wave is near its peak magnitude, thereby eliminating the possibility that voltage may be applied to the primary winding when the alternating current wave is near a zero or low value. The protective devices built into the circuit 10 to eliminate damage from high voltage transients assure protection for the electronic components of the circuit.

While the preferred embodiment of the present invention has been shown and disclosed herein, it should be understood that various changes, adaptations and modifications may be made therein without departing from the spirit of the invention and the scope of the appended claims.

What is claimed is:

l. A variable frequency electric fencecharging circuit for use with an alternating current source and a conductive fence wire for charging the fence wire to restrict movement of various types of livestock, comprising:

a firing circuit including input terminals, a silicon controlled rectifier with a gate, and a step-up transformer with primary and secondary windings, said silicon controlled rectifier electrically connected in series with said primary winding and connectable across the alternating current source, said secondary winding defining the output of said firing circuit and being electrically connectable between the fence wire and ground;

a triggering circuit, including an oscillator, said oscillator having input and output terminals and being provided with means for selectively establishing a plurality of distinct predetermined output frequencies and said frequency establishing means being substantially unaffected by impedance variations in the fence wire caused by livestock contact with the wire, the output terminals of said oscillator electrically connected to said gate of said silicon controlled rectifier to selectively bias said gate to an open condition, permitting current flow from the alternating current source to said primary winding, thereby inducing stepped up voltage in said secondary winding and charging the fence wire; and

said triggering circuit further including a diode and capacitor, said diode energizable from the alternating current source, and connected in parallel with said capacitor and in series to the input terminal of said oscillator to energize said oscillator in synchronization with the alternating current source such that said oscillator develops and delivers periodic output pulses biasing said gate of saidsilicon controlled rectifier to an open condition as the alternating current source nears a peak voltage magnitude to thereby apply the voltage to said primary winding of said transformer.

2. The electrical charge circuit of claim 1 and further including a varistor electrically connected in said firing circuit, said varistor constructed to provide a shunt across the alternating current source in response to power line surges from the alternating current source which are in excess of voltage levels capable of damaging the charging circuit, thereby protecting the charging circuit from such power line surges.

3. The electrical charging circuit of claim 1 wherein said triggering circuit includes a combined triggering and monitoring device providing a closed circuit across said device in response to the voltage across said device reaching a predetermined value and producing a visual indication when said device is conducting, permitting an operator to visually determine that said triggering circuit is biasing said gate to an open condition.

4. The variable frequency electric fence charging cirmanual introduction of one of said impedance elements into said oscillator to selectively vary the oscillator output frequency.

6. A variable frequency electric fence charging circuit for use with a current source and a conductive fence wire for charging the fence wire to restrict movement of various types of livestock, comprising:

a firing circuit including input terminals, a silicon controlled rectifier with a gate, and a step-up transformer with primary and secondary windings, said silicon controlled rectifier electrically connected in series with said primary winding and connectable across the current source, said secondary winding defining the output of said firing circuit and being electrically connectable between the fence wire and ground;

a triggering circuit, including an oscillator energizable by the alternating current source, said oscillator having input and output terminals and being provided with means for selectively establishing a plurality of distinct predetermined output frequencies and said frequency establishing means being substantially unaffected by impedance variations in the fence wire caused by livestock contact with the wire, the output terminals of said oscillator electrically connected to said gate of said silicon controlled rectifier to selectively bias said gate to an open condition, permitting current flow from the alternating current source to said primary winding, thereby inducing stepped up voltage in said secondary winding and charging the fence wire.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,868,545 Dated February 25, 1975 Inventor s) Thomas E ron It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Abstract, L. 2

Delete "charge" and substitute --charging--.

Col. 1, L; 19 Delete "to particular" and substitute --to the particular.

Col. 1, L. 44

Delete "lightening" and substitute --lightning--.

Col. 1, L. 45 Delete "voltage" and substitute --voltages--.

Col. 5,

Col. 6, L. 32'

Delete "oscillator along" and substitute --oscillator 42,

being delivered to the oscillator- Col. 7, L. 23 Delete "applies" and substitute --applied--.

Signed and Scaled this twenty-second Day Of July I975 [SEAL] A nest:

RUTH C. MASON C. MARSHALL DANN A -fli g Office Commissioner of Parents and Trademarks UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent NO 3 ,868, 54-5 Dated Februgrv Zj 1975 Inventor s) Thomas E ron It is certified that error appears in the aboveidentified patent and that said Letters Patent are hereby corrected as shown below:

Abstract, L. 2 Delete "charge" and substitute --charging--.

Col. 1, L; 19

Delete "to particular" and substitute --to the particular-.

Col 1, L. 44 Delete "lightening" and substitute --lightning--.

Col, 5, L. 8 Delete "may" and substitute --must--.

Col. 6, L. 32-

Delete "oscillator along" and substitute --oscillator 42,

being delivered-to the oscillator- Col. 7, L. 23 Delete "applies" and substitute --applied--.

Signed and Scaled this twenty-second Day of July 1975 [SEAL] A nest:

RUTH C. MASON C. MARSHALL DAN" 8 ff Commissioner of Parents and Trademarks 

1. A variable frequency electric fence charging circuit for use with an alternating current source and a conductive fence wire for charging the fence wire to restrict movement of various types of livestock, comprising: a firing circuit including input terminals, a silicon controlled rectifier with a gate, and a step-up transformer with primary and secondary windings, said silicon controlled rectifier electrically connected in series with said primary winding and connectable across the alternating current source, said secondary winding defining the output of said firing circuit and being electrically connectable between the fence wire and ground; a triggering circuit, including an oscillator, said oscillator having input and output terminals and being provided with means for selectively establishing a plurality of distinct predetermined output frequencies and said frequency establishing means being substantially unaffected by impedance variations in the fence wire caused by livestock contact with the wire, the output terminals of said oscillator electrically connected to said gate of said silicon controlled rectifier to selectively bias said gate to an open condition, permitting current flow from the alternating current source to said primary winding, thereby inducing stepped up voltage in said secondary winding and charging the fence wire; and said triggering circuit further including a diode and capacitor, said diode energizable from the alternating current source, and connected in parallel with said capacitor and in series to the input terminal of said oscillator to energize said oscillator in synchronization with the alternating current source such that said oscillator develops and delivers periodic output pulses biasing said gate of said silicon controlled rectifier to an open condition as the alternating current source nears a peak voltage magnitude to thereby apply the voltage to said primary winding of said transformer.
 2. The electrical charge circuit of claim 1 and further including a varistor electrically connected in said firing circuit, said varistor constructed to provide a shunt across the alternating current source in response to power line surges from the alternating current source which are in excess of voltage levels capable of damaging the charging circuit, thereby protecting the charging circuit from such power line surges.
 3. The electrical charging circuit of claim 1 wherein said triggering circuit includes a combined triggering and monitoring device providing a closed circuit across said device in response to the voltage across said device reaching a predetermined value and producing a visual indication when said device is conducting, permitting an operator to visually determine that said triggering circuit is biasing said gate to an open condition.
 4. The variable frequency electric fence charging circuit of claim 1 wherein said oscillator further includes a manually actuated switch and first and second impedance elements, said switch electrically connected to said first and second impedance defining elements to alternately vary the impedance of said oscillator and thereby create two predetermined, distinct output frequencies for said oscillator.
 5. The variable frequency electric fence charging circuit of claim 4 wherein said switch is a single-pole double-throw switch and electrically connected to said first and second impedance elements to permit alternate manual introduction of one of said impedance elements into said oscillator to selectively vary the oscillator output frequency.
 6. A variable frequency electric fence charging circuit for use with a current source and a conductive fence wire for charging the fence wire to restrict movement of various types of livestock, comprising: a firing circuit including input terminals, a silicon controlled rectifier with a gate, and a step-up transformer with primary and secondary windings, said silicon controlled rectifier electrically connected in sEries with said primary winding and connectable across the current source, said secondary winding defining the output of said firing circuit and being electrically connectable between the fence wire and ground; a triggering circuit, including an oscillator energizable by the alternating current source, said oscillator having input and output terminals and being provided with means for selectively establishing a plurality of distinct predetermined output frequencies and said frequency establishing means being substantially unaffected by impedance variations in the fence wire caused by livestock contact with the wire, the output terminals of said oscillator electrically connected to said gate of said silicon controlled rectifier to selectively bias said gate to an open condition, permitting current flow from the alternating current source to said primary winding, thereby inducing stepped up voltage in said secondary winding and charging the fence wire. 